Signal-receiving circuits



SIE-

lllll lllll April 9,1929. F, A KOLSTER 1,708,182 SIGNAL RECEIVING CIRCUITS Filed June 24, 1926 Patented Apr. 9, 1929.

UNITED STATES PATENT OFFICE.-

FREDERICK A. KOLSTER, OF PALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A. CORPORATION OF CALI- FORNIA.

SIGNAL-RECEIVING- CIRCUITS.

Application filed June 24,

My invention relates broadly to high frequency electron tube amplification circuits and more particularly to a high frequency amplification system having means for preventing the setting up of undesired oscillations in the electron tube circuits of the a1nplification system. One of the objects of my invention is to provide a system of multi-stage electron tube radio frequency amplification where means are connected in the successive circuits of the amplification system for preventing the flow back of energy with the inherent generation of oscillations in the high frequency amplification system.

"Still another object of my invention is to provide a high frequency amplification system including a plurality of electron tubes where means are inserted in the grid circuits of each of the electron tubes for preventing the flow back of interfering energy in the successive tube circuits while permitting the increase'in amplitude of the high frequency signaling energy through the successive 5 stages of amplification without interference.

Still another object of my invention is to provide a high frequericyelectron tube amplification system comprising a plurality of electron tubes coupled successively one to anof each of the amplification stages offering a high apparent resistance to currents at the shortest wave length to be received which automatically reduces in value as the received wave length increases for preventing the undesired generation of oscillations in the amplification circuits.

A still further object of my invention is to provide a circuit arrangement for high frequency amplification systems including a plurality of electron tubes with a circuit comprising parallel connected inductance and resistance inserted in the grid leads of each of the tubes for establishing a high value at short wave lengths where feedback is most likely to occur and smaller value at long wave lengths where feedback is less likely to'occur.

Other and further objects of my invention will be understood from the specification hereinafter following by reference to the accompanying drawings in which:

Figure 1 diagrammatically illustrates a radio frequency amplification system embodying the principles of my invention; and

other with means connected in the grid leads 1926. Serial No. 118,246.

Fig. 2 is a theoretical diagram explaining the operation of the circuit arrangement of my invention.

In a radio frequency amplifier system including a plurality of electron tubes with input and output circuits successively coupled one to another there is a tendency for amplified energy in one electron tube circuit to partially feed back'to a preceding electron tube circuit by virtue of the inherent capacity and resistance existing between the plate and grid electrodes. This energy flow back causes undesired oscillations particularly at shorter wave lengths. I

Attempts have been made to overcome these undesirable effects by neutralizing or balancing out methods, but the circuits em-- ployed are relatively complicated and diflicult to assemble in quantity production of radio receiving apparatus. By my invention, however, I provide a method which prevents rather than neutralizes the flow back of energy by inserting in the grid leads of the successive stages of electron tube amplification a parallel circuit, one portion of which consists of inductance and the other portion of which consists of resistance. The value of inductance and resistance are so proportioned and chosen as to give at the shortest wave length to be received a high apparent resistance which automatically reduces in value as the received wave length increases.

Referring to the drawings in detail, reference characters 1, 2 and 3 represent electron tubes having grid, filament and plate electrodes arranged in the successive stages of a radio frequency amplification system. Each of the electron tubes is provided with input and output circuits interconnecting the grid, filament and plate electrodes. The input circuit of the radio frequency amplification system is represented at 4 including the primary winding 5 of a high frequency transformer '6 having secondary 7 inductively coupled with the primary winding 5; The secondary 7 connects with the input circuit of'the elec tron tube 1 which is tuned by means of variable condenser 8. The auxiliary circuit of my invention is inserted in the grid lead at 9 and consists of two parallel branches, one branch of which contains inductance L and the other branch of which contains resistance R. The output circuit of electron tube 1 includes primary winding 10 of the high frequency transallel branch circuits having inductance and resistance as shown. The output circuit of electron tube 2 contains primary wlndlng 15 of high frequency transformer 16 with sec-' ondary winding 17 coupled to the winding 15 and connected in the input circuit of the electron tube 3 in series with the auxiliary circuit 18; The auxiliary circuit 18 includes parallel branch circuits having inductance and resistance elements arranged as indicated. The output circuit of the electron tube 3 contains the primary winding 19 of high frequency transformer 20 having secondary winding 21 from which extends connections to any desired number of succeeding stages of amplification or to adetector system.

I have represented several stages of amplification as having independent A and B battery systems for the purpose of more clearly explaining the invention, but it will be understood that the usual circuit arrangement may be provided for supplying space current and filament heating current froma common source.

The circuit L, R, therefore, inserted in the grid lead has the desired characteristics of introducing a high resistance impedance in the grid lead for the short waves gradually and automatically reducing its value of resistance or impedance as the wave length is increased.-- The successive amplifier circuits are variably and selectively tuned to the wave length which it is desired to receive while the circuit L, R, remains permanently fixed in its value.

The impedance of this parallel arrangement L, R varies with frequency; it is high at high frequencies or' short wave lengths and lower at low frequencies or longer wave lengths. Therefore, at short wave lengths where feedback between circuits 2 and 1 is most likely to occur, the circuit L, R is effec-. tive in preventing such feedback, while at low wave lengths where feedback is less likely, the impedance of circuit L, R is automatically reduced to a suitablevalue.

Fig. 2 represents more clearly the action of the electrical circuits in the amplifying system of my invention. I have illustrated the characteristic curve of ea-ch of the circuits 9-14 and 18 plotted against coordinates of frequency resistance and reactance. It will be observed that as the frequency increases, that is, as the wave length becomes shorter, the impedance of the. circuit is larger while at ,low frequencies orjfllong wave lengths, the

I desire it to be understood that modifications in detail may be made and that no limitations upomthe invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A signal receiving system including a plurality of electrontubes each having grid, filament and plate electrodes, input and output circuitsinterconnecting said electrodes with the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube, and a pair of parallel branch circuits connected in the input'circuits of said electron tubes, one of said branch circuits including inductance and the other of said branch circuits including substantially pure resistance for the prevention of the flow back of undesired oscillatory currents while permitting the free transfer of signaling energy at a selected frequency through said plurality of electron tubes.

2. In a signal receiving system the combination of a plurality of electron tubes each having grid, filament and plate electrodes, input and output circuits interconnecting said electrodes, the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube, means for selectively tuning said input circuits to a desired signaling frequency and means connected in series with each of said input circuits comprising inductance shunted by a resistance, the impedance of said means varying at a predetermined rate in accordance with the selected frequency and having a high impedance at high frequencies and a lower impedance at low frequencies for permitting. the free transfer of signaling energy at a selected frequency through the circuits of said electron tubes.

3. In a signal receiving system the combination of a plurality of electron tubes each having grid, filament and plate electrodes, input and output circuits interconnecting said electrodes, the output circuits of one electron tube interlinked witlithe input circuit of a succeeding electron tube, variable. means for selectively adjusting said input circuits to a desired signaling frequency and a circuit having a pair of parallel branches connected between said variable means and the grid electrodes of said electron tubes, said parallel branches including concentrated inductance and resistance elements connected in shunt with the values thereof selected to give at the shortest signaling wave length to be received a high apparent resistance which automatically reduces in value at a predetermined rate as the received wave length increases for permitting the transfer of signaling energy at a predetermined frequency through the circuits of said electron tubes.

4. In a signal receiving system the combination of a plurality of electron tubes each having grid, filament and plate electrodes, input and output circuits interconnecting said electrodes, the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube, variable means for selectively tuning said input circuits to a desired signaling frequency, and fixed means comprising inductance shunted b resistance located in said input circuits an arranged to establish a high selected impedance at high frequencies Where a tendency of feedback of energy between one electron tube and a preceding electron tube circuit exists for preventing such feedback while at lower se lected frequencies Where the tendency of feedback is less than the impedance of said means is automatically reduced at a predetermined rate to a lower value for the free transfer of signaling energy through said electron tubes thereby preventing flowback of energy and interference from local oscillations.

In testimony where of I aflix my signature.

FREDERICK A. KOLSTER. 

